Bokuda, a more advanced technique if you want the utmost in precision, is to cut the exact shapes you want to mold, into blocks of foam, making both the female and the male parts in foam first. Then wet the balsa really well, for a couple hours at least, until very pliable. Dry it with paper towels and then place the balsa in the "foam mold press" and let it dry overnight. Next night finish the iinstallation. The amount of internal structure this technique needs in very minimal.

Compound curves would be tough to do this way, but simpler shapes that can be accurately cut in foam, make prime candidates for molded balsa sections

For built up wings, the same technique may be used to actually mold the leading edges of the wing or stab. No balsa LE sticks are needed, the accuracy is terrific and the weight is the least possible.

MattK